The production of ice in aqueous liquids has many useful purposes. Thus, ice can be produced and used immediately, or the ice can be stored and used later, for cooling purposes. Also, in the production of potable water, sea water and brackish water can be cooled to produce ice, the ice separated and then melted to give the desired fresh water. Fruit and vegetable juices are also concentrated by cooling them to produce ice and then separating the ice from the concentrated juice.
The production of ice for the described purposes, as well as others, can be achieved in a number of ways including indirect heat transfer in a shell and tube freeze exchanger. A refrigerant can be used as the cooling medium on the shell side of the freeze exchanger. This method is disclosed in U.S. Pat. No. 4,286,436.
Another method of producing ice is to directly contact the aqueous liquid with a refrigerant. Direct contact heat transfer requires a reduced temperature difference between the vaporizing refrigerant and freezing solution than does indirect heat transfer systems to achieve the same energy transfer due to the elimination of the heat exchanger surface. However, the exact temperature difference required in the direct contact heat exchanger will depend upon several factors including the properties of the two fluids, the ratio of the two fluids and agitation. This method, as well as apparatus useful therefore, is disclosed in U.S. Pat. Nos. 3,017,751; 3,017,752; 3,259,181; 3,835,658; 3,885,399 and 4,046,534. After the ice is produced it is separated and then discarded, melted and used as potable water or melted to recover stored refrigeration. The refrigerant used for cooling and ice formation is recovered to the extent possible and then reused in the process.
Experience has shown that the refrigerant feeding device used for feeding the refrigerant into the aqueous liquid body has a tendency to clog due to the formation of ice on and around the feeding device and orifice through which the refrigerant flows and expands. To prevent these ice formations it has been proposed to apply resistant heating to the refrigerant feeding device as shown in U.S. Pat. No. 3,672,182. The use of resistance heating represents a persistent energy consumption. Accordingly, it would be desirable in the production of ice, by directly contacting an aqueous liquid with a refrigerant, if the refrigerant feeding device could be maintained free of ice without the use of additional energy.
Experience has also shown that a significant amount of refrigerant is lost in direct contact methods because refrigerant vapor and liquid is encapsulated or entrapped in the ice crystals. When the ice is later melted or disposed of, some or most of the encapsulated refrigerant is lost. Additionally, encapsulation of the refrigerant constitutes an economic loss of potential cooling capacity which would otherwise produce additional ice. Accordingly, it would be desirable in the production of ice, by directly contacting an aqueous liquid with a refrigerant, if refrigerant encapsulation in the ice could be reduced and even substantially eliminated.
The subject invention provides means for preventing ice formation on refrigerant feeding devices and preventing or reducing encapsulation of refrigerant in the ice.